Keep in mind that some TDS meters only read up to 2000 PPM. I have a cheap Hanna and it stops at 2000, so if I want to grow something that can take a super heavy PPM, Im outta luck.

I'd check out a shop like wormsway, or amazon.com, or if you do buy from a petshop online Ive had great results from Dr Fosters and Smith and PetSolutions.com

You can also find some deals on Ebay but I'd buy new up there, dont buy a used one unless it's from a friend that took care of it

Also get some calibration solution!! My site has some details on how I use my PH and TDS meters in my "water quality writeup"

-Eric

Here is a link that might be useful: http://www.TechnologyGarden.net

If you want a TDS meter, just get a truncheon. Hit up eBay and get a new one off there for about $40. They're factory calibrated so you don't have to mess with them.

Buy one now or buy one later, but once you've got one you won't want to own anything else.